This invention relates to a three-dimensional tool path determination method and, more particularly, to a three-dimensional tool path determination method well-suited for application to an NC data creating apparatus for a machine tool, such as a milling machine, having three or more axes, or to a numerical control device for controlling the machine tool.
In a machine tool such as a milling machine, a tool is made to approach a workpiece from a predetermined position (e.g., a reference point), numerically controlled machining is executed by the tool in accordance with a command upon completion of the approach, and the tool is retracted to a predetermined position (e.g., the reference point) after machining. For this reason, NC data for approach and retraction are always required to precede and follow NC data for transporting the tool while the tool is in contact with the workpiece. There are various tool paths for the approach and retraction of the tool, with the optimum approach path or retraction path being determined in such a manner that the tool will not strike the machine or workpiece during the approach or retraction. These approach paths or retraction paths consist of a plurality of blocks.
Accordingly, in creating NC data for an approach path or NC data for a retraction path, the conventional method includes steps of (1) deciding a tool path comprising a plurality of blocks in such a manner that the tool does not strike the machine or workpiece, (2) deciding the end point of each block and the feedrate up to the end point, and (3) entering these end points and feedrates. Thus, creating the NC data for an approach path and the NC data for a retraction path is a troublesome and time-consuming operation.